The present invention relates generally to stimulation of body tissue for a therapeutic effect on body organs, and more particularly to electrical stimulation of neurons for improving renal function.
The kidneys are essential organs located at the back of the abdomen on each side of the spinal column at about the level of the lower ribs. The kidneys receive about twenty percent of total cardiac output and function to remove waste products from the blood and regulate blood electrolytes, acid-base balance, total body water, and blood volume.
The basic functional unit of the kidney is the nephron. Each nephron includes a glomerulus, a capillary through which blood flows and from which fluid is filtered. Filtered fluid enters the tubules, which process the fluid. At the end of the tubules, the filtered fluid ultimately becomes urine. The standard measure of renal function is the glomerular filtration rate, or the total rate that fluid is filtered from all the glomeruli combined. The normally functioning kidney controls the blood electrolytes, acid-base balance, total body water, and blood volume by adjusting the reabsorption (back into the body) or secretion (from the body into the filtered fluid) of electrolytes, acids and bases, and water. If excess water is present in the body, it is excreted in the urine. If excessive solutes are present in the body, they are excreted preferentially. In spite of large intakes of either water or salt, the normal kidney can accommodate and precisely regulate the volume and composition of the blood.
Although the primary measure of kidney function relates to excretion it is important to note that the kidneys also function to produce hormones. The kidneys are in part responsible for the conversion of Vitamin D to its active metabolite, a hormone that functions to increase the absorption of calcium from the intestines. The kidneys also synthesize erythropoietin, a stimulating hormone for red blood cell production, and renin, a hormone involved in the regulation of sodium reabsorption and the maintenance of blood pressure.
Proper elimination of sodium from the body is one of the critical functions of the kidney. Failure of the kidneys to adequately eliminate sodium increases total body sodium and water, and blood volume. The increase in blood volume raises pressure in the vascular system, producing hypertension, or high blood pressure.
Progressive renal failure, occurring as a result of a variety of disorders, can give rise to a number of symptoms which decrease both the length and quality of life. Vascular damage to the glomeruli, infiltration of the renal tissues with inflammatory cells, and damage and scarring of the tubules, all contribute to the degeneration of renal function. Pathological processes primarily affecting the vasculature, such as diabetes mellitus, hypertension, overuse of over-the-counter anti-inflammatory medications, and side-effects of some pharmaceutical agents, preferentially damage the glomeruli. Chronic inflammation, repeated infection, or certain poisons may damage the tubular system. Renal failure is typically characterized by a progressive inability to maintain normal electrolyte composition, blood pH, and body water volume. Sodium chloride, or salt, becomes progressively more difficult to eliminate from the body. Concomitant interactions increase blood volume and pressure, cause acidosis, and produce edema in body tissues.